LEAD MINES OF PEOSTA AND DUBUQUE.--In my researches into the mineral geography of Missouri, in 1818 and 1819, I had explored a district of country between the rivers Merrimak and St. Francis, and on the Ozarks, which revealed many traits which it has in common with the Upper Mississippi. There, as here, the mineral deposits appear to be, in many cases, in a red marly clay, whether the clay is overlaid by the calcareous rock or not. There, as here, also, the limestone and sandstone strata are perfectly horizontal. The leads of ore appear, in this section, to be followed with more certainty, agreeable to the points of the compass; but this may happen, to some extent, because the practice of mining on individual account, with windlass and buckets, in the Missouri district, has led common observers to be more indifferent to exact scientific methods. To say that the digging, at these mines, is equally, or more productive, is perhaps just. Capital and labor have been rewarded in both sections of the country, in proportion as they have been perseveringly and judiciously expended. I found much of the ore, which is a sulphuret, at Dubuque's Mines, lying in east and west leads. These leads were generally pursued in caves, or, more properly, fissures in the rock. In one of the excavations which I visited, the digging was continued horizontally under the first stratum of rock, after an excavation had been made perpendicularly, through the top soil and calcareous rock, perhaps thirty feet. The ore is a broad-grained cubical galena, easily reduced, and bids fair very greatly to enhance the value and resources of this section of the West. Similar mines exist at Mississinawa, and the River Au Fevé,[232] both on the eastern or left bank of the Mississippi. And a system of leasing or management, such as I have suggested for the Missouri mines, appears equally desirable. [232] GALENA has subsequently been made the capital of these mines. QUARTZ GEODES.--The amount of silex in the cliff limestone is such, in some conditions of it, as to justify the term silico-calcareous. This condition of the rock at the passage of the Mississippi through the Rock River and Des Moines Rapids, is such as to produce a very striking locality of highly crystalline quartz geodes, which accumulates in the bed of the stream. Many of these geodes are from a foot to twenty-two inches in diameter, and on breaking them they exhibit resplendent crystals of limpid quartz. Sometimes these are amethystine; in other cases they present surfaces of chalcedony or cacholong. The latter minerals, if obtained from the rock, and before unduly hardening by exposure, would probably furnish a suitable basis for lapidaries.